Lecture 18 Chromosomal Mutations

Question 1

Chromosomal mutations
(Three categories with 2 examples each)

Answer 1

loss of genetic material
Deletion
missing chromosomes

Gain of genetic material
Extra chromosome
Duplication

Relocation of genetic material
Translocation
inversion

Question 2

Chromosome deletion/Del (df)
Types (2)
Effects
Mechanism (2)

Answer 2

Intragenic: small deletion within gene
Multigenic: many genes deleted

Genetic imbalances
Heterozygotes Del viable, but might results in haploinsufficient
Homozygotes Del inviable

X-ray
(Homozygous del) deletion loop

Question 3

Chromosome duplication
Types (two categories with 2 types each)
Effects (3)

Answer 3

Tandem duplication:duplicated right next to the initial gene.
Same order
Reverse order

Nontandem (dispersed) duplication: duplicated at another location on the chromosome
Same order
reverse order

Less likely to affect phenotype, but in some cases:
1. Breakpoint within genes
2. Dosage effects/genetic imbalance: overexpression of genes due to increased copies.
3. Genes being placed in a new location that modifies their expression

Question 4

Chromosome inversions
types
effects

During meiosis: crossing over in inversion loop
(Why does inversion loop form?)
(Where does crossing over occur when inversion loop present?/how does inversion loop alter where crossing over occurs)
Note:
Products
Effects of chromosome inversion in cell division where crossing over occurs

Answer 4

Pericentric inversion (include centromere)
Paracentric inversion (does not include centromere)

Less likely to affect phenotype, but in some cases:
Breakpoints within genes
Genes being placed in a new location that modifies their expression

Alleles pairing between homologous chromosomes
Crossing over occurs within the inversion loop (the inverted region) when there is inversion loop present.

Note: even though both sister chromatids of the inverted chromosome participate in the formation of inversion loop, only one sister chromatid will exchange genetic products with the other homologous chromosome if crossing over occurs.

Paracentric inversion
Products:
Normal product
Acentric fragment (lost during the process)
Deletion products (from dicentric fragment)
— will pass through 2 centromeres
Inversion products

Pericentric inversion loop
Products:
Normal product
Deletion/duplication products
— will only pass though one centromere
Inversion product

1. Breakpoints within genes
2. Gene imbalances

→ inviable gametes

Question 5

Translocation
Types (3)
Effects

During meiosis: segregation pattern of type 3 translocation
(Why this arrangement would occur)
Effects of translocation in cell division

Answer 5

Nonreciprocal intrachromosomal translocation
Nonreciprocal interchromosomal(non-homologous chromosomes) translocation
Reciprocal interchromosomal translocation

Less likely to affect phenotype, but in some cases:
Breakpoints within genes
Genes being placed in a new location that modifies their expression

Alternate — viable

Pairing alleles between homologous chromosomes
Adjacent 1
Adjacent 2
— genetic imbalances, inviable